Rigify - Envelopes look huge
Envelope distance can be set in the properties panel, selecting bone options in pose mode. If you select more than one bone, you can enter a new distance value and  keep pressed Alt key before using Enter to validate the new value, so to assign the new value to all selected bones.
Anyway using bone envelope is just one of the binding methods, the most common is using vertex weights, with automatic weights and/or weight painting and/or direct weight assignements.